Chemically-resistant adhesives and labels

ABSTRACT

Chemically-resistant adhesives formed using non-hydrolyzable hard and soft resins. Chemically-resistant labels are provided by using the adhesive to adhere an image-bearing film of polyvinyl chloride to a protective film, and to a carrier. The labels are particularly resistant to acids and have a reduced tendency to shrink or distort when affixed to battery surfaces at elevated temperatures.

BACKGROUND OF THE INVENTION

This invention relates to adhesives and labels which are resistant tochemical degradation and are capable of resisting shrinkage anddistortion when affixed to surfaces having relatively high temperatures.

Where long life and protection from abrasion and solvent or chemicalattack have been desired, it has been customary to employ metalnameplates or labels covered with a protective layer, such as a plasticfilm or a heat-cured coating of epoxy resin. Labels of this kind arerelatively expensive and sometimes difficult to apply. In addition, theyoften are inadequate in withstanding relatively high temperatureexposure and attack by chemicals such as battery acids.

Thus, plastic film and heat-cured overcoatings typically are appliedmaking use of relatively expensive ovens to produce heat which canadversely affect or distort underlying layers. Even where the labels canwithstand indirect heating, if they are affixed to a surface which issubject to constant or intermittent heating, the result can beshrinkage, distortion and curling, as well as discoloration.

Accordingly, there is a need for economical pressure-sensitive adhesivesand labels which are resistant to chemical degradation and at the sametime able to withstand relatively high temperatures. The inventionprovides for such products by using specifically formulatedadhesive-containing resins in a novel arrangement of coating layers.

It is a principal object of the invention to provide adhesives andlabels which are resistant to chemical degradation as well as shrinkageand distortion at elevated temperatures. A related object is to provideresistance to battery acids, as well as resistance to shrinkage anddistortion at the temperatures where batteries commonly operate. In thecase of vehicles, this requires the ability to withstand temperaturesclose to the boiling point of water.

It is another object of the invention to provide adhesives and labelswhich have a reduced tendency to discolor or undergo mechanicaldegradation. A related object is to resist bodystock and laminatedegradation of adhesives and labels which are subject to battery acidexposure.

Other objects of the invention will become apparent from the disclosurewhich follows.

SUMMARY OF THE INVENTION

The integrity of conventional labels is modified, and in some instancestotally destroyed, when the labels are subjected to battery acid orelevated temperatures. It has been found that these difficulties may besignificantly curtailed by using an adhesive containing non-hydrolyzablehard and soft resins. The adhesive can be applied to a non-plasticizedhomopolymer polyvinylchloride material to provide a resistant labelstructure.

Standard labels for batteries typically include a number of distinctivelayers. At the outermost position there is normally a protectivepolyester or polypropylene film that is adhered to an imprintedsubstrate by an acrylic adhesive. The latter commonly contains acrylicacid, an acrylic acid ester, or an acrylated resin, such as an acrylatedepoxy or polyetherpolyisocyanate. The imprinted substrate usually is aplasticized vinyl film on a rubber base. A standard plasticizer is aphthalate ester, and the rubber base contains a standard resin adhesive,such as that provided by "Stabelite" ester resins. Unfortunately, manyof the materials used in conventional battery labels, including inks,are able to withstand adverse effects of battery acid over a limitedtemperature range, typically up to about only 150° F. There are alsoadverse secondary effects.

Adhesives and labels in accordance with the present inventiondemonstrate improved resistance to acid degradation at relatively hightemperatures, as high as about 190° F., and the labels are unaccompaniedby discoloration and curling. This is achieved by an adhesivecomposition comprised principally of hard and soft resins. The adhesiveis used in conjunction with a non-plasticized unsubstituted pigmentedwhite film of polyvinyl chloride homopolymer. The reasons for theappreciable improvement in the stability of the resulting adhesives andlabels is not fully understood, but it has been theorized that there isan interaction in the adhesive and with the homopolymer.

An adhesive in accordance with the invention is formed from a rubberbase binder, a non-hydrolyzable hard resin tackifier, a non-hydrolyzablesoft resin plasticizer, and a stabilizer.

A variety of copolymers are suitable for the practice of the invention.They have a Mooney viscosity index of between about 35 and 55.Particularly suitable are styrene copolymers including styrene-butadieneand polyisobutylene. It will be appreciated that other similar styreneand polyisobutylene copolymers may be employed.

Binders that were evaluated and found unsuitable for the practice of theinvention include acrylics, polyvinyl ether adhesives, acrylicadhesives, block polymers, natural rubber and styrene isoprene/naturalrubber which are normally employed in rubber base binders.

An appropriate adhesive tackifier for the invention is one whichincreases adhesive tackiness without being hydrolyzed in the presence ofacid. Hard resins having a softening point in the range from about 80°C. to about 100° C. are suitable, such as those available commerciallyfrom Reichold Chemicals, Inc. under the tradename "Super Sta-Tac 80."They are pale-colored thermoplastic olefinic resins derived frompetroleum and used as tackifiers for natural and synthetic rubbers.

The adhesive plasticizer is also non-hydrolyzable in the presence ofacid. In addition, it has a softening point in the range from about 5°C. to about 10° C. and functions in combination with natural orsynthetic rubbers and resins. A soft resin plasticizer sold by Hercules,Inc. under the tradename "Piccolyte C-10" has been found to beparticularly useful. "Piccolyte C-10" is a proprietary terpene monomerderived from d-Limonene, a terpene hydrocarbon.

Other resin plasticizers such as "Piccolyte A-10" derived from d-pinene,"Piccolyte D-10" derived from dipentene, "Piccolyte S-10" derived fromB-pinene and "ADTAC B-10" which is an aliphatic hydrocarbon resin ofpetroleum origin have been found to be unsuitable. It is believed thatthe unpolymerized character of "Piccolyte C-10" accounts at least inpart for its particular suitability.

The adhesive stabilizer may be any commonly employed compound orcombination of compounds. High potency, non-staining antioxidants whichare resistant to leaching are particularly desirable. Examples are2,2'methylene bis (4 methyl-6-t-butyl phenol), 4,4'butylidene bis,6-t-butyl-m-cresol, polymerized dihydrotrimethyl quinoline, octylateddiphenylamines. A preferable antioxidant is "Wingstay-L," a commerciallyavailable polymeric-hindered phenol.

The ratio of certain components is critical in the adhesive. Thus theratio of weight of binder to tackifier must be on the order of about 1:1to about 1:1.5. However, the ratio by weight of tackifier to plasticizermay range from about 6:1 to about 15:1, with the stabilizer usuallybeing present at a concentration of about 0.5% to 3% by weight of thebinder and tackifier combination. In a preferred embodiment of theinvention the binder and tackifier are present in a weight ratio ofabout 1:1.5, with the tackifier and plasticizer being present in aweight ratio of about 12:1. The stabilizer is preferably a concentrationof about 1% by weight of the binder and tackifier combination.

The concentration of solvent for the adhesive is not critical nor is thetype of solvent. Generally, any commonly employed aromatic or aliphaticsolvent is appropriate.

Antioxidants, fillers, and other additives, preferably acid resistant,may also be used.

The carrier for the image-bearable film is provided by a substrate inthe form of a release sheet or the surface to which the label isadhered. The release sheet may be of the type conventionally used forpressure sensitive label sheet stock, with a silicone-coated paperrelease sheet being preferred.

Labels in accordance with the invention are produced by applyingpressure sensitive adhesive, formulated as described above, in solutionas a continuous web to an imprintable homopolymer film and dried.Thereafter, a release sheet is applied to the film to form apressure-sensitive adhesive laminate.

The laminated stock is then slit into proper widths for printing on apress. Although the label imprint may be made upon plasticized vinylfilm, and certain non-plasticized vinyls with any commonly employed ink,the acid resistance of the resultant label is not as great as thatachieved with polyvinyl chloride homopolymer. It also is preferable touse commercially available acid-resistant inks.

After printing, the laminate is joined to a protective polypropylenefilm, usually ranging in thickness from about 0.5 mils to about 5.0mils, by adhesive of the kind described above. The composite material isthen cut into individual, spaced labels on the release sheet.

Usually the skeleton between and around the individual labels isstripped off and uncut release sheet to leave a plurality of spacedlabels mounted on the release sheet strip, usually in one or more rows.In some cases, the release sheet may be perforated and feed holespunched into the release sheet on the labels themselves. Theseoperations, including the stripping step, are carried out at high speed.

DETAILED DESCRIPTION

For a clearer understanding of the present invention, reference is madeto the following examples which are directed mainly to the preparationof the adhesive.

EXAMPLE I

An acid-resistant adhesive is prepared from the following ingredients:

A rubber base binder of styrene isoprene copolymer

"Super Sta-Tac 80"--a tackifier with a softening point in the range fromabout 80° C. to about 100° C.

"Piccolyte C-10"--a plasticizer with a softening point in the range fromabout 5° C. to about 10° C.

"Wingstay L"--a stabilizer

Heptane and Toluene--solvents

The binder has a Mooney viscosity in the range from about 35 to 55 andis employed with the tackifier in a weight ratio in the range from about1:1 to about 1:1.5. The plasticizer has a weight ratio in the range fromabout 1:6 to about 1:15 with the tackifier; and the stabilizer has aconcentration in the range from about 0.5 to 3% weight of the combinedbinder and tackifier.

The "Wingstay L" stabilizer is dissolved in about 8 lbs. of toluene andcombined with an additional 32 lbs. of toluene and 125 lbs. of heptaneunder constant stirring conditions in a 55 gallon drum. The rubber basebinder is then added and the entire mixture stirred for about 6 hoursuntil the binder goes into solution. The "Super Sta-Tac" tackifier isnext added to the stabilizer/binder solution and stirred for about 1hour until complete dissolution of the tackifier is achieved.

The "Piccolyte" plasticizer is combined in a separate container with anamount of toluene sufficient to allow the plasticizer to go intosolution. This is then added to the homogeneous mixture of stabilizer,binder and tackifier and the entire composition stirred for about 1/2hour.

The resultant adhesive composition is pressure sensitive with aplasticity of about 1.80, a solids concentration of about 35% and aviscosity of between about 2000 to 3000 cps.

EXAMPLE II

The adhesive composition of Example I is used to form a test label. Thelabel has an outer polypropylene layer of about 1 mil. thickness,followed in succession by an adhesive layer, an image layer, a polyvinylchloride homopolymer layer of about 4 mil thickness, and anotheradhesive layer. The resultant label is applied to a substrate andevaluated against a conventional pressure sensitive battery labelcontaining an acrylic adhesive with test label proving unexpectedlysuperior.

Specifically, when the labels, each measuring about 1"×2", are affixedto a polypropylene battery case with a surface temperature of about 190°F. for approximately 24 hours, the test label demonstrates no evidenceof discoloration, curl, or acid burn. However, the conventional labelbecomes blackened around its entire outer rectangular extremity by aciddegradation over more than 40% of its surface after only 24 hours. Inaddition, significant curling and separation of the conventional labelfrom the surface of the battery itself is noted, along with appreciablehydrolysis of the imprint.

EXAMPLE III

The method of preparation and evaluation of Examples I and II areemployed using the following ingredients:

Styrene isoprene copolymer--Mooney viscosity of 40-45

Binder/"Super Sta-Tac 80" tackifier ratio--1:1.5

Tackifier/"Piccolyte C-10" plasticizer ratio--12:1

"Wingstay L" stabilizer--1% concentration

After evaluation the test labels under the test conditions of ExampleII, stability against degradation, discoloration and curl is noted ascompared with conventional battery labels.

EXAMPLE IV

An acid resistant adhesive is prepared in accordance with Example I withpolyisobutylene elastomers substituted for styrene isoprene copolymer.The resultant adhesive provides satisfactory resistance to acids.

EXAMPLE V

A test label is formed in accordance with Example II withpolyisobutylene substituted for styrene isoprene copolymer. Theresulting labels are found to be acid resistant.

The foregoing description and examples are given by way of illustrationand are not intended to limit the invention which extends to allequivalents and is defined in the following claims:

I claim:
 1. An acid resistant member comprising a non-plasticized filmof a polyvinyl chloride homopolymer secured at one side to a balancedbiaxially oriented film and at the opposite side to a substrate by anadhesive, said adhesive comprising a binder selected from the classconsisting of styrene isoprene copolymers and polyisobutylene elastomershaving a Mooney viscosity index between about 35 and 55, anon-hydrolyzable resin tackifier, a non-hydrolyzable resin plasticizer,and a stabilizer, said binder and tackifier being present in a weightratio in the range from about 1:1 to about 1:1.5, said tackifier andplasticizer being present in a weight ratio in the range from about 6:1to about 15:1, and said stabilizer being present in a concentration inthe range from about 0.5% to about 3% by weight of the binder andtackifier combined.
 2. The member of claim 1 wherein the resin tackifieris a thermoplastic olefinic resin petroleum derivative.
 3. The member ofclaim 1 wherein the resin plasticizer is a terpene monomer derived fromd-Limonene with a softening point range of about 5° C. to about 10° C.4. The member of claim 1 wherein the stabilizer is a polymeric-hinderedphenol high potency, non-staining antioxidant.
 5. The member of claim 4comprising a label wherein said stabilizer is selected from the classconsisting of 2,2'methylene bis (4 methyl-6-t-butyl phenol),4,4'butylidene bis, 6-t-butyl-m-cresol, polymerized dihydrotrimethylquinoline, and octylated diphenylamines.
 6. The member of claim 1comprising a label wherein said balanced biaxially oriented film is ofpolypropylene.
 7. The label of claim 6 wherein the thickness of saidfilm is in the range from about 0.5 mils to 5.0 mils.
 8. The label ofclaim 6 wherein said substrate is of polypropylene.
 9. The label ofclaim 8 wherein said substrate is a battery.
 10. The member of claim 1comprising a label wherein said resin tackifier has a softening point inthe range from about 80° C. to about 100° C.
 11. The member of claim 1comprising a label wherein said plasticizer is unpolymerized.
 12. Themember of claim 1 comprising a label wherein the tackifier andplasticizer are present in a ratio of 12:1.
 13. The member of claim 1comprising a label wherein the stabilizer is present in a concentrationof about 1% by weight of the binder and tackifier combination.
 14. Themember of claim 1 wherein said adhesive includes at least oneantioxidant and/or at least one filler material.
 15. The member of claim1 comprising a label wherein said film bears an image and is temporarilyadhered to a release sheet.
 16. The label of claim 15 wherein saidrelease sheet is of silicone coated paper.
 17. An adhesive compositioncomprising a binder selected from the class consisting of styreneisoprene copolymers and polyisobutylene elastomers, having a Mooneyviscosity index in the range from about 35 to about 55, anon-hydrolyzable resin tackifier, a non-hydrolyzable resin plasticizer,and a stabilizer, said binder and tackifier being present in a weightratio in the range from about 1:1 to about 1:1.5, said tackifier andplasticizer being present in a weight ratio in the range from about 6:1to about 15:1, and said stabilizer being present in a concentration ofabout 0.5% to about 3% by weight of the binder and tackifier combined.18. The composition of claim 17 wherein the hard resin is athermoplastic olefinic resin petroleum derivative.
 19. The compositionof claim 17 wherein the soft resin plasticizer is a terpene monomerderived from d-Limonene with a softening point range of about 5° C. toabout 10° C.
 20. The composition of claim 17 wherein the stabilizer is apolymeric-hindered phenol high potency, non-staining antioxidant. 21.The adhesive composition of claim 20 wherein said stabilizer is selectedfrom the class consisting of 2,2'methylene bis (4 methyl-6-t-butylphenol), 4,4'butylidene bis, 6-5-butyl-m-cresol, polymerizeddihydrotrimethyl quinoline, octylated diphenylamines.
 22. The adhesivecomposition of claim 17 wherein said resin tackifier has a softeningpoint in the range from about 80° C. to about 100° C.
 23. The adhesivecomposition of claim 17 wherein said plasticizer is unpolymerized. 24.The adhesive composition of claim 17 wherein the tackifier andplasticizer are present in a ratio of 12:1.
 25. The adhesive compositionof claim 17 wherein the stabilizer is present in a concentration ofabout 1% by weight of the binder and tackifier combination.
 26. Theadhesive composition of claim 17 further including at least oneantioxidant and/or at least one filler material.